Fuel Cycle July 2012 New

7/31/2019 Fuel Cycle July 2012 New

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The Nuclear Fuel Cycle


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Uranium

URANIUM is a slightly radioactive metal that occurs throughout the earth's

crust.

It is about 500 times more abundant than gold and about as common astin.

It is present in most rocks and soils as well as in many rivers and in sea

water.

Most of the radioactivity associated with uranium in nature is due to other

materials derived from it by radioactive decay processes, and which are

left behind in mining and milling.

Economically feasible deposits of the ore, pitchblende, U3O8, range from

0.1% to 20% U3O8.
http://www.world-nuclear.org/info/inf14.html


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Uranium Mining

Open pit mining is used where deposits are close to the surface

Underground mining is used for deep deposits, typically greater than 120m deep.

Insituleaching (ISL), where oxygenated groundwater is circulated through a veryporous ore body to dissolve the uranium and bring it to the surface. ISL may useslightly acidic or alkaline solutions to keep the uranium in solution. The uranium isthen recovered from the solution.

The decision as to which mining method to use for a particular deposit is governedby the nature of the ore body, safety and economic considerations.

In the case of underground uranium mines, special precautions, consisting primarily

ofincreased ventilation, are required to protect against airborne radiation exposure.


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Uranium Mine in Niger (Sahara Desert)


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Uranium Metallurgy

Yellowcake


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Yellowcake


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More than 200 pounds of byproduct material, tailings, are typically produced for

each pound of uranium.

After extraction of uranium from the ore, the tailings contain much of their

original radioactivity.

Toxic heavy metals, including chromium, lead, molybdenum, and vanadium, are also

present in this byproduct material in low, but significant, concentrations

Tailings from Uranium Mining and Milling


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Enriching Uranium for Reactor Fuel

Increase the concentration of fissionable U-235 isotope

Enrichment requires a physical process since

U-235 and U-238 have the same chemical properties

Physical processes require gases for separation

Uranium and its oxides are solids

Must convert uranium to UF6

Enriched UF6 must be converted back to solid

uranium or uranium oxide


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or centrifugation


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Enrichment

The two method of uranium enrichment are:

Gaseous diffusion (older)

Centrifugation (newer)

Both use small differences in the masses (< 1%) of the U-235F6 andU-238F6 molecules to increase the concentration of U-235.


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F6

F6


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Centrifuge Enrichment

FeedEnriched

exitDepleted

exit

U235F6is lighter andcollects in the center

(enriched)

U238F6 is heavier and

collects on the outsidewalls

(Depleted/Tails)

Feed toNext Stage


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The gas centrifuge process has three characteristics that make it economicallyattractive for uranium enrichment:

Proven technology: Centrifuge is a proven enrichment process, currently usedin several countries.

Low operating costs: Its energy requirements are less than 5% of the requirementsof a comparably sized gaseous diffusion plant.

Modular architecture: The modularity of the centrifuge technology allows for flexible

deployment, enabling capacity to be added in increments as demand increases.


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Fuel Fabrication

Reactor fuel is generally in the form of ceramic pellets.

These are formed from pressed uranium oxide which is sintered (baked)at a high temperature (over 1400C).

The pellets are then encased in metal tubes to form fuel rods, which are

arranged into a fuel assembly ready for introduction into a reactor.


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UF6 Gas to UO2 Powder to Pellets


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Fuel Pellets


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Nuclear Fuel Assembly

Fuel

Pellet


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Reprocessing: A Solution?

Reprocessing: The chemical separation ofspent nuclear fuel into its major components.

Wikipedia.org


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Reprocessing

Objectives

Recover U, Pu and Th to be used as fuel

Separate radioactive and neutron- absorbing

fission products

Convert the radioactive waste into suitable forms

for safe storage

The US does not have reprocessing nor a long

term storage facility.


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20

Lawrence Livermore National Laboratory

Reprocessing


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Products of Reprocessing

Uranium .6% U-235 and 99.4% U-238 Plutonium Minor Actinides

Americium

Major long-term heat source Neptunium

Major source of radiation

Curium

Fission Products

Strontium-90, Cesium-137 Generate large amounts of heat for the first 50-80 years after disposal Removal from the repository would reduce the amount of space needed

Iodine-129, Technetium-99 Mobile isotopes that can easily travel through geological formations

Major contributors of radiation to biosphere

U.S. DOE


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Three Nuclear Fuel Cycles

Once through thermal reactors

(current approach)

Recovery of plutonium for one additional

pass through thermal reactors

Repeated reprocessing and recycling ofuranium, plutonium, and other

transuranics in fast-neutron reactors


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Why Reprocess and Recycle?

Original reason (1940s-1970s):

Believed demand for nuclear power would be far greater than it

turned out to be Believed world uranium reserves were far smaller than they

turned out to be

Current reason:

Reduce amount of nuclear waste

Given the uncertainties surrounding the Yucca Mountainlicense application process

Additional uranium energy secondary


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Spent Fuel Storage Pools


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Reprocessing: Methods/Techniques

PUREX: Plutonium and Uranium Extraction Most widely used method

Results in a pure stream of plutonium

UREX: Uranium Reduction Extraction

Replacement for PUREX Results in pure uranium stream

The plutonium remains mixed with the fissionproducts and minor actinides

UREX+ Refinement of the UREX process

Pyroprocessing Reduces the liquid waste that remains in the UREX

process


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Reprocessing: Then what?

Storage in a repository, or . . .

. . . Waste Recycling

Definition: Transmuting or destroying the separatedwaste products of reprocessing. Transforms the long-lived radionuclides into short-lived ones. 12

Reprocessing alone is not sufficient to reduce thevolume and toxicity of used fuel, ensure adequatesupplies of uranium, and achieve proliferation resistance.

A transmutation program could transform the problem oflong-term isolation in a geological repository (for 10s ofthousands of years) to a less difficult problem of storagefor several decades or a few hundred years.


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Methods of Recycling

Transmutation involves inducing nuclear

reactions in some form of non-traditional

reactor.

Fast reactors

Breeder Reactors

Burner reactors

Fast Neutron Reactors


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Results of Recycling

Waste products:

No transmutation scheme is able to destroy

all of the components of spent nuclear fuel.

Most will require multiple passes through thereactor to recycle a significant amount.

Some of the components, although reduced

by volume, will be converted to moreradioactive forms.


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Benefits of Reprocessing andRecycling

The ability to reduce the volume and toxicity

of nuclear waste

A smaller, simpler repository Extension of time before a second repository is

necessary

Closed fuel cycle consistent uraniumsupply


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Costs of Reprocessing

Plutonium Stockpiles/WeaponsProliferation

Environmental and health harms

Terrorism Transportation of high level waste

Reactor safety, worker health

Economic cost

New regulatory schemes


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Mixed Oxide Fuel (MOX)

MOX is produced from the output of reprocessing plants and is a mixture of

plutonium and uranium oxides with a composition of 3% to 7% PuO2 and the rest

UO2

. The MOX is then mixed with ordinary LEU uranium-oxide fuel for use in light

water reactors. Mixture is 1/3 MOX and 2/3 LEU.

By 2001, over 20 power reactors in France were using MOX for one third of their

fuel In the US, MOX fuel is being used as a means of disposing of Pu from

dismantled nuclear weapons in the US and Russia.


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Fuel Reprocessing Plant, Marcoule, France


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Relative Costs

Process $/kg fuel

Uranium $500

Conversion $50

Enrichment $600

Fabrication $250

Wet storage Included in capital & O%M

Dry cast storage $200

Geological storage $400

Total Cost $2000

Fuel Cycle July 2012 New

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